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Old 10-27-2009, 11:25 PM   #1
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Default Help! Cylinder 4 not firing...

I'm having a weird issue with my MS build.

At first, it was missing on cyl 1 + 4. I pulled the COP and saw spark jumping to the valve cover so it is getting spark. What confuses me is that 1+3 and 2+4 get fuel together, so that made me think it's not a fueling issue.

I then found the thread about people having issues with hi-res and the 1k ohm resistors so I swapped them to the 270 ohm resistors like this diagram, as well as adding the capacitor as this diagram shows:


Heres a picture of my board before doing the cap and swapping resistors.


Tried it again and cylinder 1 was firing. Now its down to cylinder 4. This confused me as 1+4 fire together as wasted spark. I pulled the MS again and inspected the board. Found a short.
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In the lower right where I have the red circle, the spark 1+4 wire was touching the bottom solder of the resistor that is right there but on top of the PCB.... R25 I believe.

Any idea what damage I may have done?
I need to fix this ASAP to get the race car running and tuned in time.

Thanks for any help you can provide.
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Old 10-28-2009, 10:03 AM   #2
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if 1 is firing but 4 isn't, it's gotta be the coilpack.

I'm sure Joe will chime in with extensive info on the ramifications of the spark signal touching the resistor; but touching the part of R25 means you might have sent 5v or current straight out to the coilpack. This could have damaged either the coilpack or ignitor or both. (This is what we try to avoid when flashing the MS unit and why we unplug the coilpacks)

If you need a new coilpack (90-93) I can mail you out one to test, unless you can source locally.
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Old 10-28-2009, 11:09 AM   #3
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It's not the coilpack. Have COPs, Swapped coils from a firing cylinder: didn't change anything. Swapped ECUs: fixed it.

This is also for a 94.
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Old 10-28-2009, 11:14 AM   #4
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replace the transistor on that circuit (q8), see what happens. Keep your spares? otherwise you can steal one from q13 or q10 so long as you're not using the PWM code for low-ohm injectors which I assume you're not.
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Old 10-28-2009, 06:22 PM   #5
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Replaced Q8.... Cyl 1 and 4 not firing.
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